Process for condensing vapors from gas mixtures



Dec. 3, 1935. F. POLL ITZER ET AL 2,022,732

PROCESS FOR CONDENSING VAPORS FROM GAS MIXTURES Filed April 20, 1954 A v5 AT a 1, J M a .l FYiL ll 2 1 v4. 1/

Patented Dec. 3, 1935 UNITED STATES PROCESS FOR CONDENSING VAPORS FROMGAS MIXTURES Franz Pollitzer, Grosshesselohe, near Munich,

and Paul Schuitan, Munich, Germany Hollriegelskreuth, near ApplicationApril 20, 1934, Serial No. 721,644 In Germany April 24, 1933 7 Claims.(Cl. 62-175.5)

The present invention relates to a process for separating easilycondensable constituents from gas mixtures by cooling and condensation.According to the invention the gases are cooled in periodically changedcold accumulators down to the dew point of the vapors. The furthercooling and the condensation of the vapors is performed in separatecoolers by means of a refrigerating machine, e. g. a multiple stageammonia refrigerating machine. The gas escaping from the last cooler hasa temperature far below the dew point of the vapors in the fresh gas; itis, therefore, not possible to utilize the cold of this gas completelyin the regenerators, as in this case a portion of the vapors to beobtained would be condensed in the cold accumulators and, afterreversing, would be carried along by the escaping gas. The cold residualgas, therefore, according to the presentinvention, is reheated beforeentering the regenerators up to a sufliciently high temperature toprevent a condensation of the vapors from the fresh gas. An advantageousway of performing this reheating of the residual gas is to bring it intoheat exchange with the refrigerant of the refrigerating machine, thustransmitting the cold contained in the residual gas to the refrigerant.

I The new process presents important advantages in comparison with theprocesses used heretofore. By replacing the usual counter-current heatexchangers by the cold accumulators energy is saved as well on accountof the smaller loss of pressure of the gases while passing the exchangeras by the higher efficiency of cold recovery, the heat of vaporizationbeing completely transmitted in the regenerators from the incoming tothe outgoing gas. Other processes proposing to use regenerators withlong periods could not make use of these advantages and diminish thelosses of cold.

The invention will be more particularly described as applied to theseparation of benzene from coal distillation gases with reference to theaccompanying drawing which is a diagrammatic representation of a systemof apparatus embodying the invention.

The gas, precooled and freed from the chief quantities of tar andnaphthalene, is cooled, in the cold accumulator 2, respectively I, downto the dew point of the benzene in the gas, for example, at a content of25 grams per cubic meter down to 18 C. Then the gas enters the cooler 3of known construction which is cooled by evaporation of carbon dioxideor ammonia; here it is cooled until the benzene is condensed to theextent desired. The cooler in which the benzene is separated, isprovided in duplicate in the usual manner (3 and 4 in the drawing). Whena certain quantity of benzene is condensed in a cooler the gas flow isreversed to the other cooler by 5 means of valves 8 and 9, and the firstcooler is heated to melt off the benzene frozen-out. The flow of the gasand of the refrigerant in the period after reversing coolers 3 and 4 isshown by the dotted lines. This heating is suitably 10 effected by usingthe cold contained in the cooler so that the cooler serves not as anevaporator, but as a condenser for the refrigerant. The refrigerantflows in one period as shown in the drawing from the compressor 6through water cooler 1 where it is condensed and is undercooled in thecooler 5 and then evaporated in 3 or 4, respectively, where the benzeneis condensed. In order to melt out the benzene condensedin 3 or 4,respectively, after reversing the coolers, a portion of the volatilerefrigerant, leaving compressor 6, is condensed in this cooler and thenadded to the portion of the refrigerant liquefied in I.

The gas leaving the cooler 3, respectively 4, is warmed in thecounter-'current cooler 5 in heat exchange with the refrigerant up toabout the dew point of the benzene in the fresh gas and then flows outagain through the cold accumulator l, respectively 2.

The gas freed from the benzene can be reheated by the cooling agent insuch a manner that a portion of the cooling agent is liquefied not atthe temperature of cooling water and correspondingly high pressures, butat low pressures in heat exchange with the cold gas; I In multiple stagerefrigerating machines that portion of the cooling agent which iscondensed at low temperatures, is drawn from the first or second stageof compression. Another working method 40 consists in liquefyingthecooling agent in the usual manner at the temperature of coolingwater, and undercooling it by heat exchange with the cold gas before theevaporation. Both methods of transmitting the cold may be utilizedtogether. Finally, the reheating of the gas escaping from the cooler 3,respectively 4, may also take place in such a manner that, between thecold accumulators and this cooler, a heat exchanger is intercalated inwhich an exchange of cold between the fresh gas and the gas freed fromthe benzene takes place. i The gas escaping from this exchanger may thenbe introduced into the regenerators without a condensation of benzenetaking place in them. The counter-current cooler is preferably provideddoubly so that one cool er is in operation while the other one is freedfrom the constituents which condense in solid form.

Particularly when obtaining benzene the use of regenerators for coolingthe gas is of great advantage, as in this case the separation of thecondensates occurring above the dew point of the benzene takes placereversibly so that for this purpose no special demand of cold isrequired. On the one hand, these condensates have but a low commercialvalue, and on the other hand, their remaining in the gas is sometimesdesirable as they preserve a protecting layer on the pipings the absenceof which would, otherwise, cause severe troubles in valves, etc., bydeposits of rust and dust.

The new process is of special advance for obtaining benzene if apreceding purification of the gas from naphthalene, especially bycooling to about 0 C., has taken place. In this case the gas ispractically completely freed from tar and naphthalene and also, to agreat extent, dried so that not many condensates have to be separatedand again evaporated in the regenerators. Furthermore, the gas is atdisposal in precooled condition. The purification of the gas by coolingto about 0 C. may be very advantageously combined with the describedseparation of benzene if for the latter cooling multiple-stagecompression refrigerating machines are used. In this case the coldrequired for prepurifying the gas is furnished in a simple andeconomical manner by the middle pressure stage of the compressionrefrigerating machine.

The purification of the gas from sulphur which in most cases isnecessary, may take place be fore or after the benzene has beenseparated. If the purification is performed after the separation ofbenzene, the purification mass can be' utilized in a very favorabledegree owing to the high purity of the gas. If the purification takesplace before the separation of benzene, a henzene free from sulphur isobtained. As for the usual purification from sulphur the gas is requiredin a warm and moist condition it is suitable, if the purification fromsulphur is to be intercalated between a purification of the gas bycooling and the separation of benzene, to reheat the gas which comescold and dry from the purification, in countercurrent heat exchange withthe warm and moist gas which comes from the purification from sulphurand, at the same time, to moisten it, so that it will transmit its coldand'dryness to the gas free from sulphur.

We claim:

1. Process for condensing vapors from gas mixtures which comprisescooling the gas mixture in periodically alternated regenerators down tothe dew point of the vapors to be condensed,

condensing the vapors by further cooling by heat exchange with thevolatile liquid refrigerant of a refrigerating machine, warming thegases after the condensation of the vapors by heat exchange with thevolatile refrigerant and passing the warmed gases through the aforesaidregenerators.

2. Process for condensing vapors from gas mixtures which comprisescooling the gas mixture in periodically alternated regenerators down tothe dew point of the vapors to be condensed, condensing the vapors byfurther cooling by heat exchange with the volatile liquid refrigerant ofa. refrigerating machine, warming the gases after the condensation ofthe vapors by condensing a portion of the volatile liquid refrigerantand passing the warmed gases through the aforesaid regenerators.

3. Process for condensing vapors from gas mix tures which comprisescooling the gas mixture in periodically alternated regenerators down tothe dew point of the vapors to be condensed, con densing the vapors byfurther cooling by heat exchange with the volatile liquid refrigerant ofa refrigerating machine, warming the gases after the condensation of thevapors by heat exchange with the volatile liquid refrigerant which ishereby undercooled and passing the warmed gases through the aforesaidregenerators.

4. Process for condensing vapors from gas mixtures which comprisescooling the gas mixture in periodically alternated regenerators down tothe dew point of the vapors to be condensed, condensing the vapors byfurther cooling by heat exchange with the volatile liquid refrigerant ofa refrigerating machine, warming the gases after the condensation of thevapors by heat exchange with the fresh gas leaving the regenerators in aseparate counter-current heat exchanger and passing the warmed gasesthrough the aforesaid regenerators. I

5. Process for condensing benzene from gas mixtures which comprisescooling the gas mixture in periodically alternated regenerators down tothe dew point of the benzene, condensing the benzene by further coolingby heat exchange with the volatile liquid refrigerant of a refrigeratingmachine, warming the gases after the condensation of the benzene by heatexchange with the refrigerant and passing the warmed gases through theaforesaid regenerators.

6. Process for condensing benzene from gas mixtures which comprisespurifying the gas mixture from naphthalene, cooling it in periodicallyalternated regenerators down to the dew point of the benzene, condensingthe benzene by further cooling by heat exchange with the volatilerefrigerant of a refrigerating machine, warming the gases after thecondensation of the benzene by heat exchange with the refrigerant andpassing the warmed gases through the aforesaid regenerators.

7. Process for condensing benzene from gas mixtures which comprisespurifying the gas mixture from naphthalene by cooling it to about 0 C.,cooling the gas mixture in periodically alternated regenerators down tothe dew point of the benzene, condensing the benzene by further coolingby heat exchange with the volatile liquid refrigerant of a refrigeratingmachine, warming the gases after the condensation of the benzene by heatexchange with the refrigerant and passing the warmed gases through theaforesaid regenerators.

FRANZ POLLITZER. PAUL SCHUFIAN.

